I dont hang around here that much anymore. But to answer your question, its all about the efficiency and capacity that plants can process light. Large scale cultivators will strive to maximize on both of these in order to increase their profit margins as much as possible. Using the data we have on cannabis photosynthesis, we know that the quantum yield (photosynthetic efficiency) is highest and linear from the compensation point up to around 500umols. With a non linear decline above this level until around 1000umols, where any additional energy becomes practically useless and unused (excess energy which is lossed through heat disspitation methods such as non photochemical quenching). The excess light energy can actually have a negative quantum yield, where photosynthesis can be lower at higher intensities than at lower intensities.
The sweet spot is around 700-800umols (around 80,000 lux), which allows the most effective use of light but also to maximize production of the plant. To accomodate the average flux density (PPFD) of this intensity, requires the flux (PPF) energy of around the same values per square metre. This is roughly 450w per square metre with typical DE gas diacharge. The true representation of a light source is its flux value (PPF). Not its flux density value (PPFD). In fact practically all PPFD measurements are false, as it misrepresents its own definition and true intention of use. Where light is required to be uniform in all directions in order to gain accurate intensity values, which is calculated for a specific surface area (per square meter). PPFD as they are traditionally used by people in horticulture, are in fact spot measurements only, which can only provide valuable information for the size of the measurement sensor which is used, and thats it.
I could go all day but id rather not, if you have any further questions. Find me outside here, where i spend more of my time on.
